Electrotransport drug delivery devices have a wide range of application for transdermal delivery of therapeutic medicaments to individuals. Passive transdermal drug delivery systems employ a chemical concentration gradient and electrically-assisted (ie, electrotransport) transdermal drug delivery systems employ an electric field under control of an electronic controller to drive charged drug ions from a reservoir placed adjacent to the surface of the skin, through the skin (or a mucosal membrane) and into the bloodstream or body tissues.
Transdermal drug delivery systems are placed on the skin for some prescribed time period (eg, 24 hours) during which drug is delivered. In electrotransport devices, the transdermal drug flux, at least at certain applied current densities, is proportional to the level of applied current. The electrotransport drug flux can be controlled by controlling the magnitude and timing of the applied current. Thus, electrotransport devices afford greater control of transdermal drug flux than passive transdermal delivery systems. Because the magnitude of applied electrotransport current is typically quite low (eg, less than 150 .mu.A/cm.sup.2), the patients generally cannot feel the applied electrotransport current. This can create some uncertainty, at least in those electrotransport devices having no on/off indicator (or other means for signaling when the device is on and applying electrotransport current), since neither the user (patient) nor the clinician have any immediate indication that the drug is being delivered as prescribed. A malfunction of the device may not be detected during use. An example of a malfunction may simply be that the system has run out of drug and therefore cannot continue to deliver drug at the prescribed rate.
In response to these problems, many electrotransport systems incorporate visual or audible displays to communicate the status or operating conditions to the user or clinician. See for example, Maurer et al, U.S. Pat. No. 5,254,081, FIG. 3 element 70 shown as LEDs and buzzer; Bannon et al U.S. Pat. 5,135,480 FIG. 2 showing LCDs; Haak et al U.S. Pat. No. 5,246,417 showing LEDs, FIG. 5, elements 63-1 to 63-n; Sorenson, US SIR H71; DeVane UK Patent GB 2 239 803 A; and Brodard EP 0092015 October , 1983, showing a speaker for sounding an alarm.
The audible and visual displays of the prior art devices typically create lights or tones which may compete with similar lights and sound in crowded environments, creating the possibility that the display may be unnoticed. In some environments, for example, a quiet hospital ward, it may be undesirable to have disturbing or annoying lights or sounds. With visually-impaired or hearing-impaired patients, lights or sounds may not always be noticeable. Thus, there is a need for a means for notifying a patient of an electrotransport device condition without using visual or audible signals.